The invention relates to eye replacement implants. If an eye has become damaged due to trauma or disease, the damaged eye may have to be eviscerated in which all of the inner contents of the eye are removed, or an enucleation may be performed in which the entire eyeball is removed after severing it from the eye muscles and the optic nerve. Following either of these procedures, it is common practice to fill the resulting void with an orbital implant and subsequently fit to the implant an ocular prosthesis that closely resembles the eye. When properly placed within the orbit, the orbital implant replaces the volume lost when the eye was removed and helps to maintain the normal structure of the eyelids and eyebrows. When the ocular prosthesis is properly matched to the other eye and coupled to the implant to move with it, substantially normal appearance of the patient is restored.
A variety of orbital implants have been used and are known and available, usually taking the form of a sphere or globe of suitable inert material. When the implant has been inserted following enucleation or evisceration of the eye, tissues will heal over the implant after which the ocular prosthesis is placed on the tissues that have formed over the implant. However, over a period of time, migration and extrusion of the implant can occur. In the integrated implants first used in the 1950s, the primary cause of implant migration or extrusion was that when the ocular prosthesis was coupled to the orbital implant, it was necessary to expose a portion of the implant to the outside environment, thereby allowing bacteria to enter and infect the implant. Another cause of implant migration and extrusion is the lack of tissue supposedly covering the implant thereby allowing possible infection to enter through any opening where the implant is not covered by tissue. Also, sometimes the tissues which have previously covered the implant become pressured and necrose, thus allowing bacteria to enter and cause infection. This can occur years after the implant is made.
A number of attempts have been made to overcome these and other problems of implant migration and extrusion. Perry, U.S. Pat. No. 4,976,731 teaches the use of an orbital implant made of low density hydroxyapatite, and following implantation of the implant and during the healing process, tissue penetrates the porous structure of the implant as the scleral sac or other covering is absorbed into the system. Perry teaches that after sufficient healing has occurred, the implant can be drilled to provide a passageway that allows the ocular prosthesis to be attached to the implant by insertion of a peg protruding from and forming a part of the prosthesis. Perry asserts that this will resolve the concern of migration or extrusion of the implant because tissue will also grow into and provide a lining for the drilled passageway. However, even using the Perry recommended material for the implant, a second surgical procedure is required with the normal risks of such procedures, including infection of the tissue around the peg implant.
Vachet, U.S. Pat. No. 5,089,021, teaches the use of a spherical core over which there is bonded a layer of material made from a micro-porous, bio-compatible synthetic substance such as polytetrafluorethylene (EPTFE). Vachet claims that with this implant construction, the coating layer will be invaded by fibroblasts and blood vessels which will gradually transfer the coating layer into a tissue and vascular shell and thus minimize the risk of migration and extrusion of the implant. Vachet then asserts that following healing, the patient can be fitted with an ocular prosthesis by carefully molding the prosthesis over the tissues covering the implant. However, since the only traction between the prosthesis and the implant is from the tissues forming the posterior aspect of the socket, this technique may produce less than satisfactory motility.
In all of the prior art teachings, references are made to the use of a variety of different materials for the orbital implant which materials are all preferably inert. Also, the prior art teaches the use of materials which are microporous so that the surrounding tissue will eventually penetrate the implant to hold it in place and thereby minimize the possibility of extrusion of the implant. Perry, U.S. Pat. No. 4,976,731, referred to above is an example of this teaching. The prior art also teaches the use of different synthetic materials that are used by oral and orthopedic surgeons to replace voids created in bone structures. Brekke U.S. Pat. No. 4,186,448 is an example of such a teaching in which bone voids created by fracture, surgery, etc. are treated by filling the voids with a material that is bio-degradable and which has randomly positioned voids throughout substantially all of the its volume. Brekke also teaches the use of a wetting agent incorporated in the material to promote the filling of the voids in the material with blood vessels so as to form tissue that will fill the voids. Eventually, this material becomes absorbed.
However, prior art materials that are currently known and used for some eye implants are quite expensive, and those that are not microporous, occasionally require additional surgical procedures to minimize migration and extrusion. In addition, the known structures and techniques for integrating the ocular prosthesis with the orbital implant are not entirely satisfactory. Some such techniques require post-surgical drilling of the implant after healing has occurred adding to the cost and patient trauma and always with risk of infection.
There is therefore a need for an improved orbital implant that will reduce the surgical procedures and time involved and thus lower the cost of the overall implant process as well as provide for improved integration of the implant with the ocular prosthesis. There is furthermore a need for the use of improved materials for the orbital implant which materials will reduce greatly the likelihood of migration or extrusion of the implant.